Google’s social network, Google+, is more popular than Twitter. Every month, nearly 390 million people worldwide use the service to post messages, make video calls and endorse search results by clicking on a so-called +1 button.

And yet, two years after its launch, Google+ is still a work in progress.

Yes, a lot of people use the service, but they generally do so only briefly. Meanwhile, the search giant’s initial hopes that it would blossom into a major business have yet to pan out. The reasons are many, according to analysts, who inevitably point to Google’s late start in social networking. Some also cite a muddled purpose. Is Google+ a rival to Facebook, the social networking Goliath? Or is its mission to stitch together Google’s disparate services and make them more useful? “If I had Google in the room with me I would advise them to better communicate their vision,” says Brian Solis, a principal analyst at Altimeter Group.

To be clear, this is no time to write an epitaph for Google+. In just a short amount of time, the service has achieved quite a bit. The issues have more to do with the high expectations that come with anything Google does. Building a new social network from scratch out of the spotlight is not an option.

Google created Google+ amid growing fears about Facebook’s rapid rise. Social networking had become a key starting point for people online and a huge advertising business. But Google had missed the wave after fumbles like Buzz and Orkut. Co-founder Larry Page, who took over as Google’s chief executive in 2011, made catching up a big focus.

What Google came up with was a social network that, superficially, looks a lot like Facebook. Users can post the usual messages about their weekend plans, baby photos and links to articles they like. What makes Google+ different is its emphasis on sharing with small groups—family, friends and tennis partners, for example—rather than with all acquaintances. “Circles,” as groups are called, are designed to more closely mimic how people interact offline, Google executives said.

Over time, Google folded several existing products into Google+ like Picasa photos and local listings along with certain parts of Gmail, Maps and YouTube. Google+ is now so sprawling that many people have little choice but to use it while others are completely unaware that they are doing so.

Vic Gundotra, senior vice president of engineering for Google, has acknowledged that Google should have added a social component to its products earlier. Social networking gives the company more details about its users like their names, where they live and what they’re interested in so that the information can be used to personalize products for them.

“Google+ is the beginning of that process,” Gundotra said recently in a question and answer session with the public held on Hangouts, the Google+ video conferencing service. He added that the effort is also aimed at creating “one beautiful, simple and seamless experience” across the company’s various products. Before, users had no single identity across search, email and YouTube.

Google+ got off to a good start in terms of users, and their numbers have continued to climb. But the amount of time they spend there is surprisingly limited. U.S. visitors to plus.google.com, the main Google+ doorway, totaled 25 million via desktop computers in August, according to Nielsen, the audience measurement firm. Those users spent an average of just 5.5 minutes keeping in touch with friends. Facebook, by contrast, had 128 million U.S. people visit by desktop in the same month, Nielsen found. They averaged more than 6.5 hours a month on the service.

The comparison isn’t exactly perfect. The numbers only take into account the main Google+ site and not activity on other related services like a shortcut that appears on virtually every Google product for getting messages. But the data highlights the huge challenge Google faces. Facebook has an overwhelming head start.

Google+ did somewhat better with its mobile apps, attracting 25 million users who averaged 12 minutes on them during August. Facebook’s apps, however, had nearly 112 million users who averaged more than seven hours on the service. Google declined to discuss the disparity. Generally speaking, Gundotra said in his online chat that “Google+ is growing faster than we ever anticipated and it’s great to see the community grow across the world.”

One crucial part of Google’s strategy is to use Google+ to personalize search. Messages and photos from users’ connections often appear in response to queries. The idea is that information from Google+ may be even more relevant than the usual list of blue links. Someone looking for a review of a restaurant, for example, may want to see what a friend wrote. Google executives stress this kind of subtle benefit when talking about Google+. The goal, as they explain it, is bigger than simply helping people update their friends about tasty dinners and fabulous vacations, like they do so often on Facebook.

For example, last week, Google said it would use Google+ to help raise the quality of comments on YouTube videos. Posts from a person’s Google+ connections will appear above all others with those by the video’s creator and celebrities. Users prefer to see comments from people they care about rather than complete strangers, Google said. The switch will be made by the end of the year.

When Google first introduced Google+, some Wall Street analysts issued reports talking about the importance of the project and their expectations that it would become a huge business. Like Facebook, Google could sell more ads. But it hasn’t exactly turned out that way because Google has yet to directly monetize the service.

There are, of course, indirect benefits from Google+ like making Google search more relevant and thereby increasing usage. Information people put in their profiles can also be used to better target ads that appear on other Google products.

Solis, the analyst, said that Google still has work to do on the Google+ design. In particular, he said Google should focus on making the service more human, or easier to use. Superb engineering and data-driven design is, of course, the company’s strong point. Whether it can also excel at something as touchy feely as people sharing cat photos—or surfacing their friends’ cat photos in search results—remains to be seen.